Continuous casting machine and method for manufacturing cast slab

Abstract

To provide a drain mechanism that does not hinder drainage of cooling water from draining from each guide roll segment, in a vertical part of a continuous casting machine.SOLUTION: A continuous casting machine includes: a secondary cooling zone comprising a vertical part, a curved part, and a horizontal part in the order from a side of a casting mold, on a lower side of the casting mold; and a draining gutter for the cooling water that has been supplied to a cast slab passing through a vertical part in a longitudinal intermediate range of the vertical part.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a vertical bending type continuous casting machine, and more particularly to a drainage structure for cooling water supplied to a slab passing through a secondary cooling zone. The present invention also relates to a method for producing a slab using the continuous casting machine. [Background technology]

[0002] An example of a vertical bending type continuous casting machine is shown in Fig. 1. As shown in Fig. 1, the vertical bending type continuous casting machine has a secondary cooling zone 3 below a mold 2 to which molten steel 1 is supplied via a ladle and a tundish (not shown). That is, the molten steel 1 in the mold 2 is discharged vertically while forming a solidified shell, and is cooled and shaped in the secondary cooling zone 3 provided immediately below the mold 2 to produce a cast piece 4, a typical example of which is a slab.

[0003] In the above-described vertical bending type continuous casting machine, the vertical section 30 of the secondary cooling zone 3 plays an important role in floating and separating inclusions in the molten steel during the process of solidifying the molten steel 1. By configuring the equipment to have a long vertical section 30, high-quality steel can be produced.

[0004] As shown in Figure 1, the guide rolls that make up the secondary cooling zone 3 of the continuous casting machine are configured as guide roll segments 5, each of which consists of a first frame to which one guide roll of a guide roll pair within the segment is fixed, and a second frame to which the other guide roll of the guide roll pair is fixed.

[0005] During continuous casting, the slab is cooled mainly by contact with the guide rolls to remove heat and by cooling water sprayed from spray nozzles, and this cooling is carried out for each guide roll segment 5. In the vertical section 30, the cooling water supplied to the slab for each guide roll segment 5 hits the slab 4 and then falls to the segment 5 below it.

[0006] The vertical section 30 of the secondary cooling zone 3 is provided so as to be surrounded by a building having a plurality of chambers partitioned by pillars and beams. One guide roll segment 5 is installed for each chamber. That is, as shown in Fig. 2, which is a cross section taken along line II-II in Fig. 1, the guide roll segment 5 is composed of guide rolls 8a and 8b rotatably installed on a first frame 7a and a second frame 7b that straddle beams 6a and 6b that partition and form a chamber 6 of the building.

[0007] Furthermore, in chamber 6, floors 9a-9c are provided around beams 6a and 6b that define the chamber, allowing, for example, inspection personnel to enter. As described above, used cooling water (hereinafter referred to as cooling water without distinction between used and unused water) falls downward after being supplied to slab 4 in guide roll segments 5, with much of the cooling water falling onto floors 9a-9c. To prevent this cooling water from remaining on floors 9a-9c, floors 9a-9c are constructed with gratings having through-holes. That is, the cooling water after being supplied to slab 4 falls downward through the holes in the grating floors 9a-9c. In this way, the cooling water falling sequentially from the upper segments 5 to the lower segments 5 is typically collected and drained in bottom chamber 31, located at the very bottom of vertical section 30.

[0008] In conventional vertical bending continuous casters, used cooling water mixed with scale falling from above is collected and drained in the lowest bottom chamber. During the process of collection in this bottom chamber, scale S1 and other debris S2 frequently clog the grating floor, especially the grating floor 9a, which receives the cooling water splashing back, resulting in poor drainage. This causes the falling water to be discharged outside, deteriorating the surrounding environment and causing cracking in the semi-finished product. Furthermore, cooling water sprayed from the spray nozzles on the front and back surfaces of the slab in one guide roll segment spreads across the slab's width and flows or falls downward from the side of the slab. In continuous casters with a long vertical section, cooling water from the upper guide roll segment flows into the lower segment, causing overcooling of the slab. Because overcooling of the slab can lead to quality defects such as slab cracking, the cooling water from each guide roll segment must be drained without affecting the cooling of the subsequent guide roll segments.

[0009] Therefore, in conventional equipment, nozzles for spraying air are located at the bottom of each guide roll segment, outside the slab width edge, and a mechanism is provided to discharge the cooling water that flows or falls from the side of the slab outside the segment system. The cooling water discharged outside the system reaches a grating floor that is arranged at the bottom of the segment so as to surround it, and then falls downward from there. Summary of the Invention [Problem to be solved by the invention]

[0010] However, this mechanism could stop functioning if scale clogged the air nozzle, preventing air from being sprayed. Furthermore, the air not only blows away the cooling water but also the scale (rust) on the surface of the slab, causing the scale to clog the holes in the grating floor. Because cooling water cannot be discharged downwards from a clogged grating floor, the cooling water that accumulates on the clogged grating floor returns to the segment, causing the slab to overcool.

[0011] In particular, in continuous casting machines with long vertical sections, the lower guide roll segments are more susceptible to clogging of the grating holes than the upper segments because scale accumulates not only on the lower segments but also on the upper guide roll segments that have fallen from the upper segments.As a result, abnormal cooling can frequently occur below the vertical section (bend section), and frequent cleaning of each guide roll segment is required to prevent abnormal cooling.

[0012] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a drainage mechanism in the vertical section of a continuous casting machine that does not impede the drainage of cooling water from each guide roll segment. [Means for solving the problem]

[0013] The gist and configuration of the present invention are as follows. 1. A continuous casting machine having a secondary cooling zone below the mold, consisting of, in order from the mold side, a vertical section, a curved section, and a horizontal section, and having a drain trough in the longitudinal middle region of the vertical section for draining cooling water supplied to the cast piece passing through the vertical section.

[0014] 2. The continuous casting machine according to 1 above, wherein the drainage trough has an inclined surface that makes the flow rate of the cooling water 44.40 m / min or more.

[0015] 3. The drainage gutter is a first inclined portion extending along the guide rolls in an area adjacent to the guide rolls on the opposite side of the slab path sandwiched between the pair of guide rolls, with a width equal to or greater than the roll axial length, and having a slope downward from a start edge toward a terminal edge on the guide roll side; two second inclined portions each having a slope that slopes downward from a widthwise middle point of the terminal edge of the first inclined portion to both ends of the terminal edge of the first inclined portion in the widthwise direction; two cylindrical portions each opening at an end of the second inclined portion and extending downward; 3. The continuous casting machine according to claim 1 or 2,

[0016] 4. A method for producing a slab using the continuous casting machine described in 3 above. [Effects of the Invention]

[0017] This invention prevents the cooling water from the upper segment from flowing into the lower segment and clogging of the holes in the grating floor of the lower segment. This prevents the drained cooling water from being re-supplied to the slab, preventing overcooling of the slab. Furthermore, since scale buildup in each segment is prevented, the frequency of cleaning the chambers can be reduced. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a conventional continuous casting machine. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 10 is a diagram illustrating clogging of holes in a grating floor. [Figure 4] 1 is a schematic diagram showing the structure of a continuous casting machine according to the present invention. [Figure 5] FIG. 2 is a perspective view showing the specific structure of a drainage gutter. [Figure 6] FIG. [Figure 7] FIG. 10 is a perspective view showing a drainage gutter installed on a guide roll segment. DETAILED DESCRIPTION OF THE INVENTION

[0019] One embodiment of the continuous casting machine of the present invention is shown in Figure 4. The present invention is preferably applied to a vertical bending type continuous casting machine with a vertical section as shown in Figure 4, but it can also be applied to any casting machine in which the material is poured below the mold.

[0020] In the continuous casting machine shown in Fig. 4, the same components as those in the continuous casting machine shown in Fig. 1 are designated by the same reference numerals, and their description will be omitted. That is, the continuous casting machine shown in Fig. 4 is characterized in that a drain trough 10 for cooling water to be supplied to the slab 4 passing through the vertical section 30 is provided in the longitudinal intermediate region of the vertical section 30 of the secondary cooling zone 3 in the continuous casting machine shown in Fig. 1. The reference numeral 11 denotes an outlet pipe for discharging the cooling water received in the drain trough 10 to the outside of the system.

[0021] As described above, by providing the drain trough 10 in the longitudinal intermediate region of the vertical section 30, it is possible to temporarily collect the cooling water used in each guide roll segment 5 above the intermediate region and drain it outside the system. In other words, by temporarily draining the water while the scale in the wastewater is thickening, clogging of holes in the grating floor in the drainage path can be prevented. Furthermore, in a solidification vertical bending type continuous caster in which falling water is collected at the chamber bottom, providing a drainage position in the intermediate region also prevents overflow at the chamber bottom.

[0022] In particular, the installation position of the drain gutter 10 is preferably a position above the installation position where 75% or more of the total amount of cooling water is sprayed during casting. That is, it is preferable to install the drain gutter 10 directly below the upper segment where at least 75% of the total amount of cooling water is sprayed, and to discharge the cooling water and scale. This is because if the drain gutter is installed directly below a segment where the amount of cooling water is less than 75%, the amount of water flowing through the drain gutter will be insufficient and the flow rate will be insufficient, which may make it difficult to discharge the scale inside the drain gutter without causing it to accumulate.

[0023] On the other hand, if a drainage gutter is provided immediately above the lowest segment, where the accumulated cooling water volume from the upper segments is sprayed at nearly 100% of the total cooling water volume, there is a high risk of clogging of the grating holes in the segments above this. Therefore, it is preferable to provide the drainage gutter 10 immediately below the segment where the accumulated cooling water volume from the upper segments is sprayed at 95% of the total cooling water volume during casting, or immediately below a segment above that.

[0024] More specifically, when the vertical section is composed of 10 segments 5, operation is often carried out so that the amount of cooling water in the top five segments 5, where the solidification of the slab is in the early stages, is 75% or more of the total amount of cooling water, so it is more preferable to place a drain trough 10 directly below the top five segments 5.

[0025] Furthermore, to prevent poor discharge, the drainage gutter 10 is preferably designed so that the flow velocity in the flow path through which the cooling water passes is 44.40 m / min or more. That is, the reason why the preferred range of the flow velocity in the flow path is 44.40 m / min or more is to prevent scale and the like from accumulating in the gutter when the cooling water received in the drainage gutter 10 is discharged outside the system, and the threshold value determined by an experiment described below is 44.40 m / min.

[0026] The flow velocity in the cooling water flow path of the drainage trough 10 correlates with the amount of cooling water flowing through the flow path and the inclination of the flow path. Because the amount of cooling water supplied during continuous casting is determined for each slab being produced, the design of the flow path of the drainage trough 10 is important to achieve the above-mentioned optimum range of flow velocity for a given range of cooling water amounts. Specifically, the drainage trough 10 must be placed within the chamber 6 of the building in the horizontal direction while ensuring sufficient space for inspection personnel to enter the chamber 6. Meanwhile, the height must be lower than the height of one segment. From this perspective, we considered the design of the drainage trough 10 and found that the drainage trough 10 with the following structure is advantageous for achieving the above-mentioned optimum flow velocity while saving space.

[0027] That is, a preferred example of the drain trough 10 is shown in Fig. 5. This drain trough 10 comprises a first inclined portion 12 that extends along the guide rolls 8a and / or 8b in an area adjacent to the guide rolls 8a and 8b on the side of the vertical portion 30 opposite the path of the slab 4 sandwiched between the guide rolls 8a and 8b for a length equal to or greater than the roll axis length and that slopes downward from the starting edge toward the terminal edge on the guide roll side, two second inclined portions 13a and 13b that start at the middle in the width direction of the terminal edge of the first inclined portion 12 (the center in the width direction in the illustrated example) and slope downward toward both ends of the terminal edge of the first inclined portion 12 in the width direction, and two cylindrical portions 14a and 14b that open at the terminal ends of the second inclined portions 13a and 13b and extend downward.

[0028] Here, the first inclined portion 12 is disposed, for example, directly below the grating floor 9a of the chamber 6 in which the guide roll segment 5 is housed and in the area adjacent to the second frame 7b in Figure 2, to catch the falling cooling water. The falling water flows down the first inclined portion 12, branches off from the terminal edge of the first inclined portion 12 to flow down into the second inclined portions 13a and 13b, respectively, and finally flows down into the outlet pipe 11 below via the tubular portions 14a and 14b. Therefore, in the drainage gutter 10, it is essential to appropriately set the inclination angles of the first inclined portion 12 and the second inclined portions 13a and 13b in order to achieve the above-mentioned desirable flow velocity.

[0029] It is desirable that the width of the first inclined portion 12 be equal to or greater than the roll shaft length, and more preferably the same as the frame width of the segment, in order to recover cooling water in the width direction of the slab and at the sides of the widthwise ends.

[0030] In the drain gutter 10 having the above configuration, the inclination angle of the first inclined portion 12 relative to the horizontal plane was set to 13°, the inclination angle of the second inclined portion 13a was set to 5°, and the inclination angle of the second inclined portion 13b was set to 3°, and the flow of cooling water mixed with scale was verified. The specifications of this drain gutter 10 are shown in Table 1. All parts of the drain gutter were made of SUS304.

[0031] [Table 1] (*):See Figure 6

[0032] A drainage trough 10 with the above specifications was installed directly below the fifth guide roll segment 5 from the top (the position where 75% of the total cooling water volume was recovered) in the continuous casting machine shown in Figure 4, and continuous casting was carried out for one year. Three sizes of cast pieces were produced during this time: A size, C size, and J size, and the amount of cooling water in each part of the trough was as shown in Table 2. The cooling water from the guide roll segment 5 was supplied to the first inclined portion 12 shown in Figure 6 and allowed to flow down to the second inclined portion 13a and the second inclined portion 13b.

[0033] [Table 2]

[0034] After one year of continuous casting, the presence or absence of deposits in each part of the drainage trough was checked. The results are shown in Table 3.

[0035] [Table 3]

[0036] From the above results, it was found that sediments accumulated on the first inclined portion 12 and the second inclined portion 13b, but no sediments occurred on the second inclined portion 13a. Next, the flow velocity V [m / s] of the falling water at each part of the drainage gutter was calculated using Manning's equation (1) below. Note JPEG2025173431000005.jpg13170where n: Manning's roughness coefficient [m -1 / 3 s] (SUS304:0.012m -1 / 3 s) i: Water surface gradient (sinθ) R: Diameter depth [m]

[0037] In deriving the flow velocity V of the falling water, it was assumed that 5% of the total amount of cooling water mentioned above flows into the first inclined portion 12, and half of that flows equally into the second inclined portions 13a and 13b. Furthermore, it was assumed that the drainage gutter in the illustrated example according to the present invention has short flow paths in the first inclined portion 12 and the second inclined portions 13a and 13b, and therefore there is no difference in water depth within the gutter, and the water depth h was calculated by dividing the flow rate by the area of ​​the inclined portion.

[0038] In the above formula (1), the diameter depth R is the average water depth of the channel cross section, and is calculated by dividing the flow area by the wetted perimeter. In other words, the flow area is the area [m 2 ], and the wet perimeter is the total length [m] of the water in contact with the bottom or wall of the channel. Table 4 shows the diameter and depth R at each slope of this drainage gutter, along with the water surface gradient i. Note that the water surface gradient i is the gradient of the slope and is expressed as tan θ, but because θ is small, the value calculated by approximating cos θ ≒ 1 and using sin θ is used.

[0039] [Table 4]

[0040] The flow velocity V of the falling water at each of the first inclined portion 12 and the second inclined portions 13a and 13b of the drainage trough, calculated from Manning's equation (1) according to the above, is shown in Table 5 for each of the slab sizes shown in Table 2.

[0041] [Table 5]

[0042] The results shown in Table 5 show that deposits can be reliably avoided by setting the flow velocity to 44.40 m / min or higher. Therefore, in order to prevent scale from adhering to the drainage gutter and deposits from forming starting from these deposits, it is preferable to configure the drainage gutter so that the flow velocity of the fluid flowing through it is 44.40 m / min or higher. Incidentally, Manning's equation (1) shows that the smaller the Manning's roughness coefficient n, the greater the flow velocity V, making it less likely that deposits will occur.

[0043] Here, in the drainage gutter 10, the width of the first inclined portion 12 is preferably equal to the width of the guide roll segment 5, and the inclination angle is preferably determined by taking into account the planar area of ​​the chamber 6, the vertical height of the segment 5, and the height of the second inclined portion. On the other hand, the width of the second inclined portions 13a and 13b is sufficient if it is wide enough to recover all of the cooling water from the first inclined portion 12, and the inclination angle is preferably set so that the flow velocity is 44.40 m / min or more.

[0044] If a flow velocity of 44.40 m / min or more cannot be ensured in the first inclined section 12 by the inclination angle alone, a flow velocity of 44.40 m / min or more can be ensured by providing a fluid speed-increasing mechanism at one or more locations in the width direction of the starting edge of the first inclined section on the guide roll side. [Example]

[0045] To compare the results when drainage gutters were installed and when they were not, the "slab maintenance weight," which indicates the rate of slab quality defects per month of continuous casting machine operation, was investigated. The results showed that when drainage gutters were installed, the "slab maintenance weight" was reduced by 54% compared to when they were not installed. Here, "slab maintenance" refers to the work of removing defects that have occurred on the slab surface due to cooling abnormalities using a grinder or other tool. The frequency with which this work occurred, i.e., the frequency with which slab defects occurred, can be evaluated by the total weight of slabs that underwent slab maintenance. [Example]

[0046] Drainage troughs 10 with different inclination angles were installed in the middle section (directly below the fifth guide roll segment 5 from the mold side) of the solidification vertical bending continuous caster shown in Figure 4, directly below the grating floor 9a in the chamber and in the area adjacent to the guide roll 7b as shown in Figure 7. Various drainage troughs with different specifications shown in Table 6 were installed as drainage troughs 10, and the degree of scale accumulation was observed.

[0047] The material of the gutter is highly heat-resistant and corrosion-resistant, and the Manning roughness coefficient is 0.012m -1 / 3 The material used was SUS304, which has a low water content of 1000 s. The speed-increasing mechanism in No. 2 consisted of water sprays attached at four locations across the width of the starting edge of the first inclined section on the guide roll side, spraying at a back pressure of 0.7 MPa and a flow rate of 17.8 L / min. The flow velocity of the first inclined section in No. 2 was measured with a propeller-type current meter at the width edge on the terminal edge, i.e., the part farthest from the water sprays.

[0048] [Table 6]

[0049] As shown in Table 6, in No. 1, the calculated flow velocity of the first inclined section 12 and the second inclined section 13b was less than 44.40 m / min, and deposits were found on the slopes. On the other hand, in No. 2, no deposits were found on the slopes of either inclined section.

[0050] Incidentally, it was confirmed that temperature-related casting abnormalities were reduced by 50 tons per month when a drainage gutter was installed in the middle of the vertical section compared to when it was not installed. [Explanation of symbols]

[0051] 1. Molten steel 2. Mold 3 Secondary cooling zone 30 Vertical section 4. Castings 5 Guide Roll Segments 6 chambers 6a,6b Beam 7a, 7b frames 8a, 8b Guide rolls 9a, 9b, 9c Grating floor 10 Drainage gutter 11 Outlet pipe 12 First slope 13a,13b Second slope part 14a, 14b cylindrical portion

Claims

1. A continuous casting machine having a secondary cooling zone below a mold, which zone is composed of, in order from the mold side, a vertical section, a bent section, and a horizontal section, and a drain trough in the longitudinal middle region of the vertical section for draining cooling water supplied to a cast piece passing through the vertical section.

2. 2. The continuous casting machine according to claim 1, wherein the drain trough has an inclined surface that allows the flow rate of the cooling water to be 44.40 m / min or more.

3. The drainage gutter is a first inclined portion extending along the guide rolls in an area adjacent to the guide rolls on the opposite side of the slab path sandwiched between the pair of guide rolls, with a width equal to or greater than the roll axial length, and having a slope downward from a start edge toward a terminal edge on the guide roll side; two second inclined portions each having a slope that slopes downward from a widthwise middle point of the terminal edge of the first inclined portion to both ends of the terminal edge of the first inclined portion in the widthwise direction; two cylindrical portions each opening at an end of the second inclined portion and extending downward; 3. The continuous casting machine according to claim 1 or 2, further comprising:

4. A method for producing a cast slab using the continuous casting machine according to claim 3.

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